The present invention relates to a substrate treating apparatus suitable for cleaning and drying substrates having low mechanical strength, e.g. glass substrates and semiconductor wafers, and also relates to a method of operating the substrate treating apparatus.
Drying techniques carried out after the process of cleaning semiconductor wafers, optical discs, etc. can be generally divided into two types as follows. A first type is a technique that employs chemicals, e.g. IPA (isopropyl alcohol). A second type is a technique whereby an object to be dried is rotated at high speed to blow off droplets under centrifugal force. In addition, techniques in which a vacuum technique is combined with the first or second techniques are also employed. However, these techniques suffer from the problems stated below.
The drying method using chemicals, e.g. IPA, incurs a high costs to ensure safety as combustible chemicals are employed. Moreover, this method is liable to cause environmental pollution.
In the drying method using high-speed rotation, because an object to be dried is rotated at high speed, a centrifugal force acts on the object, and torsional stress also acts thereon during acceleration or deceleration of the rotation, causing the base material of the object to be damaged. This causes a reduction in yield. In addition, during the drying process, the base material of a substrate to be treated elutes out into contact areas between the substrate and waterdrops to form annular protuberance-shaped traces, i.e. water marks.
It has been proposed to dry a substrate by using an apparatus shown in FIG. 1. A substrate 101 to be treated (i.e. an object to be dried) is placed in a stationary state, a rotary impeller 102 is installed to face a surface of the substrate 101 and the surface of the substrate 101 is dried by rotation of the rotary impeller 102. However, this proposal has not yet been put to practical use for the following reason. That is, an outward air flow occurring on the surface of the impeller 102 produces a negative pressure at the central portion of the rotary impeller 102. Consequently, a secondary flow occurs on the surface of the substrate 101 as shown by the arrow A. As a result, a waterdrop 103 is likely to remain in the center of the surface of the substrate 101.
In addition, a rotating shaft 105 of a motor 104 for rotating the rotary impeller 102 is supported by rolling bearings 106 and 107. Therefore, if lubrication is effected with a grease which is usable in a clean environment, the upper limit value for the DN value [bearing diameter (mm).times.rotational speed (rpm)] is low, so that it is difficult to employ a rotating shaft 105 in the form of a hollow shaft.